Fog inhibitor for photographic developers



Patented July 13, 1943 FOG INHIBITOR FOR PHOTOGRAPHIO DEVELOPERS Arnold Weissberger, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing.

Application July 8, 1941,

Serial No. 401,439

12 Claims.

This invention relates to photographic developers and particularly to fog inhibiting or toning agents for developers.

It i well known that fogging occurs in a photographic film or plate when it is developed for unusually long periods of time. It is necessary in most cases to use a relatively weak developer in order to avoid the formation of fog. Soluble bromides, such as potassium bromide, have been used in the developer to overcome this but they do not permit development with a strong developer for long periods of time at temperatures which may go higher than 70 F.

I have discovered that certain derivatives of aminobenzimidazole, for example, Z-amino-G-nitrobenzimidazole and 2-amino-4,6-dinitrobenzimidazole, may be incorporated in the developer to obtain all of these advantages. These compounds may be used either in black-and-white or in color developers. In some cases they may be added to the emulsion or to the subbing or backing layers of the film or plate.

Aminobenzimidazole appears to have one or the other of the following structural formulas:

O=NH

C-NHz and N NO: H

2-amino-fi-nitrobenzimidazole has previously been prepared by Kym and Rather, Ber. 45,3254 (1912) however the melting point is given as 189-190 instead of 245-246 C. The compounds used in the present invention were prepared by essentially the method of Pierron, Ann. Chem. and Phys. (8), 15, 189-193, by reaction between o-phenylenediamine and cyanogen bromide. Z-amino-G-nitrobenzimidazole nitrate was prepared as follows:

One part of o-phenyleneguanidine was dissolved in about 20 parts of nitric acid (01. 1.42) at room temperature, and the solution allowed to stand at room temperature for 15-20 hours. The bulk of the product crystallized from the reaction mixtur during this time. An additional amount was precipitated from the reaction mixture by diluting with 2%; volumes of Water. After recrystallization from water the product formed orange-yellow needles which were highly unstable at elevated temperatures. The melting point was about 225 C. The free base melted at 245-246 C.

In a similar manner other nitro and dinitro, such as the 4-nitro and 4,6 dinitro, derivatives of aminobenzimidazole may be prepared and are contemplated for use in my invention.

The following examples, which are intended to be illustrative only, indicate developing formulas using nitro derivatives of aminobenzimidazole according to my invention.

Example 1 A black and white developer is mad as follows:

Monomethyl-p-aminophenol sulfate grams l Hydroquinone do 5 Sodium sulfite do 20 Sodium carbonate do 30 Sodium hydroxide do 1 Water to iter 1 Example 2 A developing solution for forming a colored image by coupler development is made as follows:

A 2-amino-5-diethylaminotoluenehydrochloride grams 1 Sodium sulfite do 10 Sodium carbonate do 30 Water to liter 1 B 2,4-dichloro-a-naphthol grams 2 2-amino-fi-nitrobenzimidazole do 0.2 Water to cc 100 In use, B is added to A. This developer produces a blue-green dye on development of an exposed silver halide layer. The amount of aminobenzimidazole derivatives used in either black and white or color developers may vary from about .005 gram to 0.50 gram per liter or higher.

In some cases it may be desirable to develop emulsion layers containing a coupling agent in the emulsion layer, in which case the color-forming developer would contain the fog inhibitors of the invention but would be devoid of coupling agent.

I consider as within my invention all equivalents and modifications falling within the scope of the appended claims.

What I claim is:

1. A photographic developer containing a decomprising a primary aromatic amino developing agent and a nitro derivative of Z-aminobenzimidazole.

6. A color-forming photographic developer comprising a primary aromatic amino developing agent, a coupler compound, and 2-aminobenzimidazole having at least one nitro group on the benzene portion of the molecule.

'7. A color-forming photographic developer comprising a primary aromatic amino developing agent, a coupler compound, and 2-amino-6- nitrobenzimidazole.

8. A color-forming photographic developer comprising a primary aromatic amino developing agent, a coupler compound, and 2-amino-4,6- dinitrobenzimidazole.

9. The method of preventing the formation of fog on development of an exposed silver halide layer, which comprises treating the layer with a developing solution containing a developing agent and a nitro derivative of Z-aminobenzimidazole.

10. The method of preventing the formation of fog on development of an exposed silver halide layer, which comprises treating the layer with a developing solution containing a developing agent and 2-amino-fi-nitrobenzimidazole.

11. The method of preventing the formation of fog on color-development of an exposed silver halide layer, which comprises treating the layer with a solution containing a primary aromatic amino developing agent and a nitro derivative of Z-aminobenzimidazole in the presence of a coupler compound.

12. The method of preventing the formation of fog on color-development of an exposed silver halide layer, which comprises treating the layer with a solution containing a primary aromatic amino developing agent and 2-amino-4,6-dinitrobenzimidazole in the presence of a coupler compound.

ARNOLD WEISSBERGER. 

